1. Field of the Invention
The present invention relates to a coil box apparatus provided between a roughing mill and a finishing mill at a hot rolling mill so as to wind up a rolled material transported from the roughing mill, and more particularly to a coil box apparatus to control a temperature of the rolled material at the finishing mill.
2. Description of the Prior Art
FIG. 1 is a schematic view of a coil box apparatus provided at the conventional hot rolling mill, in which reference numeral 1 designates a coil box enclosed by the broken line. A sheet steel rough-rolled by the roughing mill (not shown) at a hot rolling mill is transported in the direction of the arrow A, fed to the coil box 1, and coiled by a number of receiving rolls 2. The sheet steel transported from the roughing mill, which is different in temperature distribution from the utmost end to the tail 4, is coiled to make the temperature distribution more uniform. A sheet steel coil 5 coiled at the coil box 1, after the temperature of the entire coil becomes uniform, is fed toward (in the direction of the arrow B) a finishing mill 7 in the downstream side process of the hot rolling mill on the basis of a control signal from a controller 6 given a signal showing a condition of proceeding a rolling operation of an advanced sheet steel at the finishing mill. In this case, the sheet steel is uncoiled from the tail 4 thereof when transported in the direction of the arrow A from the roughing mill, and then fed to the finishing mill.
The coil box apparatus at the hot rolling mill, as above-mentioned, coils the sheet steel transported from the roughing mill to thereby make the temperature from the head to the tail of the sheet steel more uniform. When the coiled sheet steel sits for a long time in the coil box due to a delay of the rolling process for a preceding sheet steel, a temperature (a) of the outermost coiled layer of the sheet steel decreases more than that (b) of the inside coiled layers from the second coiled layer as shown in FIG. 2, thereby increasing a temperature difference between the outermost first layer and the inside layers from the second one with the result that variation occurs in a thickness and a width of the sheet steel during the finish rolling, thereby adversely affecting the product.